Circuit arrangement for the sending of current impulses over telephone lines



Sept. 8, 1931. v R. TRECHCINSKI 1,822,635

CIRCUIT ARRANGEMENT FOR THE SENDING 0F CURRENT IMPULSES OVER TELEPHONE LINES Original Filed March 5, 1927 Patented Sept. 8, 1931 UNITED STATES PATENT OFFICE ROMAN TRECHCINSKI, F WARSAW, POLAND, ASSIGNOR TO TELEFONAKTIE BOLAGET L. M. ERICSSON, OF STOGKHOLM, SWEDEN, A COMPANY OF SWEDEN CIRCUIT ARRANGEMENT FOR THE SENDING OF CURRENT IMPULSES OVER TELEPHONE LINES Original application filed March 3, 1927, Serial No. 172,490, and in Poland April 24, 1926.

Divided and this application filed May 29, 1930. Serial No. 457,358.

The sending of direct current impulses in rapid succession over long telephone lines is generally subjected to disturbances due to the electrical properties ofthe line, that is to say it its capacity, leakage, inductivity and resistance. Even if the impulse transmission takes place by interrupting and closing the line circuit at the sending place, it may thus occur that the current does not decrease down to zero at the receiving place but varies, during the transmission of a series of current impulses, for instance in the manner indicated on the attached drawings, Figs. 1 and 2. Said conditions are particularly pronounced in lines with a high self-induction, such as loaded lines. From a technical point of view it is impracticable to construct an impulse relay of the usual type so as to make it operate in the desired manner under such conditions. The present invention relates to a circuit arrangement, whereby said disadvantage may be eliminated and the absolutely reliable operation of an impulse relay by means of direct current impulses rendered possible also over lines where, on account of the electrical properties of the lines, the current variations at the place of reception follows the course illustrated in Figs. 1 and 2.

Theinventionissubstantiallycharacterized by that in parallel with the preferably polarized impulse receiving relay an inductance is connected up the inductivity of which eX- ceeds that of the relay so that the current through the relay, upon a decrease in the line current, will be neutralized or reversed by the extra current then induced in the closed circuit formed by the relay winding and the parallel connected inductance, the relay armature being thereby shifted. This results in a so called static safety in the relay. The relay winding is namely normally passed by a part of the line current proper whereby is ensured that the relay is brought to or held respectively in its normal position in the intervals between the impulses.

The invention will be more closely described with reference to Figs. 3 and 4, Fig. 3 showing the circuit arrangement in principle according to the invention and Fig. 4 its apwith an inductive resistance S2. The induc-.

tion coil is assumed to have a comparatively high inductivity and a comparatively small ohmic resistance in comparison with the relay PR. lVhen the line circuit is closed a current passes through PR in the direction from 11 to 10 whereby the armature 5 is held bearing against the contact 6. The stationary current in the relayis, on account of the higher resistance of the relay, comparatively small. Upon a decrease in the line current an extra E. M. F. is induced in Si which E. M. F., if exceeding the drop of voltage caused by the current through the induction coil, generates an electric current through the relay in the direction from 10 to 11 the relay armature being then shifted towards the contact 7 The relay PR is thus brought to operate by the rapid current fluctuation caused by the current impulses in the relay circuit but not by the absolute value of the line current or by those comparatively slow current variations which are unable to generate the potential difference required to shift the relay armature. The position of the relay armature depends, in other words, upon the current derivate the armature bears against the normally closed contact and at a negative it dt against the normally open contact. The cir- At a positive euit arrangement shown in Fig. 3 may also be used in an ordinary neutral, i. e. unpolarized, relay. If the line current at the receiving place does not decrease to the value zero upon an interruption of the line circuit at the sending place, the extra current from the induction coil in an arrangement accord ing' to Fig. 3 will neutralize or counteract respectively the relay current so as to cause a sufficient variation in the current to deenergize said neutral relay.

The circuit arrangement shown in principle in Fig. 3 may, of course, be practically carried out in many different manners using inductances in different combinations. Instead of induction coils also electromagnetic relays may be used which, at the same time, may be used for different switching purposes.

Fig. lshows an application of. the invention in an automatic telephone system and illustrates a circuit arrangement for connecting the impulse relay to junction lines provided with a microphone feeding bridge and also a speaking transformer and a blocking condenser, as the case may be. In the application of the invention already existing inductances in such a junction line may be advantageously used in connecting up the re In the arrangement according to Fig. l the polarized relay PR is thus connected in parallel to the one of the choke coils I I in cluded in the microphone feeding bridge, a circuit arrangement being then obtained which substantially corresponds to the arrangement according to Fig. 3. The letter A designates the subscribers apparatus and L.

the subscribe1"s line which in ordinary manner over a pre-selcctor is connected to a unction line FL connected to the microphone battery over the terminals 3, l. The junction line contains besides a speakingtransformer Tr and a blocking condenser C. The portion of the junction line including the secondary winding of the transformer T1 is controlled by the relay PR over the normally closed contact 6. During impulse sending the relay PR is actuated in the same manner as that described with reference to Fig. 3 and transfers impulses from the subscribers line to the latter portion of the junction line.

I claim:

1. A circuit arrangement for transferring selector impulses over telephone lines, especially loaded lines, comprising in combination with an impulse receiving relay, an inductance connected in parallel therewith and having a higher inductivity than that of the relay so that, upon a decrease in the line current, an extra current is induced in the closed circuit formed by the winding of said relay and said parallel connected inductance, said extra current opposing the normal relay current to such an extent that the relay armature is shifted.

ROMAN TRECHCINSKI. 

